The present invention relates to a paper separating unit to firmly prevent from more than one sheet of paper from being fed at a time, and an electronic printing apparatus which has the paper separating unit.
FIG. 1 is a perspective view of a paper feeding unit disposed in an electrophotographic device manufactured by FUJITSU LIMITED.
As shown in the perspective view of FIG. 1, this paper feeding unit is to prevent more than one sheet of paper P from being fed at a time (it is referred to as a multiple-feeding for later description in this specification), using a separate roller 3, as it picks up the paper P from a paper container where the paper is contained by a pick roller 1, then feeds the paper into a gap between a first feed roller 2 and the separate roller 3.
Therefore, the pick roller 1 and the first feed roller 2 are driven by a motor 4 in the same rotational direction (here the direction is that their lower perimeter of the pick roller 1 and the first feed roller 2 rotate from the pick roller 1 side to the first feed roller 2 side). On the other hand, while being pressed onto the first feed roller 2 with a predetermined magnitude of force, the separate roller 3 is driven by said motor 4, in the same direction as that of the first feed roller 2.
A torque limiter 5 is placed between this motor 4 and the separate roller 3, and when more than one sheet of the paper P attempt to pass through the gap between the first feed roller 2 and the separate roller 3, a rotational force generated by the separate roller 3 is applied on the second and lower sheets of paper P, and it generates a slip between the first paper P and the second paper P, then separates them apart, only the first sheet of paper P is pushed out from between the first feed roller 2 and the separate roller 3. However if only one sheet of paper P is fed into the gap between the first feed roller 2 and the separate roller 3, the separate roller 3 would be driven by the first feed roller 2 through this paper P without disturbing feeding of the paper P while it rotates in the opposite rotational direction as that of the first feed roller 2.
As the paper P which has passed through the gap between the first feed roller 2 and the separate roller 3 is fed to a second feed roller 6, the second feed roller 6 is driven to acceleratedly feed the paper P while said motor 4 is stopped.
Each of two one-way clutches 7, 8 is interposed between the first feed roller 2 and the motor 4 which drives the first feed roller 2, and between the pick roller 1 and the motor 4 respectively. After the motor 4 is stopped, the first feed roller 2 and the pick roller 1 are driven by the paper P which is acceleratedly fed by the second feed roller 6 in the paper feeding direction.
On the other hand, at the separate roller 3, friction is caused and it stops the separate roller 3 when the motor 4 is attempted to be rotated so that it gives a resisting force to the paper P, preventing the multiple-feeding.
However, This might be happened that when the second feed roller 6 described above is driven, and the paper P passing through the gap the first feed roller 2 and the separate roller 3 is strongly pulled in its feeding direction, the motor 4 is driven via the separate roller 3 to rotate in the reverse direction by this paper P which is acceleratedly fed. In this case, since the first feed roller 2 and the pick roller 1 freely rotate in the paper feeding direction from the motor 4 due to the one-way clutches 7, 8, the multiple-feeding can occur as more than one sheet of paper P are fed into the gap between the first feed roller 2 and the separate roller 3.
Besides, to improve the capability of the paper separating, it is effective to increase a predetermined torque of the torque limiter 5; however, the higher the predetermined torque of the torque limiter 5 is set, the higher the probability of the reverse-rotation of the motor 4 becomes which moves along with the separate roller 3 when the second feed roller 6 accelerates feeding of the paper P.
As a method to prevent the reverse-rotation of the motor 4 as above, a method may be arise wherein the first feed roller 2 and the separate roller 3 are continuously driven without the accelerated feeding by the second feed roller 6 until the back end of the paper P passes through the gap between the first feed roller 2 and the separate roller 3.
However, in order to increase the operational speed of the apparatus, this method cannot be taken since it is advantageous to acceleratedly feed the paper P immediately after the front end of the paper P passes through the gap between the first feed roller 2 and the separate roller 3, when feeding the paper P out of the paper container which is located far from a printing portion, especially where the paper container is made multi-tiered.
As another method to prevent the multiple-feeding, a method may be arise wherein the rotational speed of the pick roller 1, the first feed roller 2, and the separate roller 3 is increased while accelerating the feeding of the paper P.
However this method cannot be taken either, since it inevitably causes enlargement of the drive system which drives those rollers and complication of their control devices, thus it cannot avoid a cost increase as a result.
Moreover, as a method other than described above to prevent the multiple-feeding, a method may be arise wherein i.e., fixing the separate roller 3 without driving it as disclosed in the Japanese Patent Application Laid-Open No. 6-171783 (1994). However, this method is not favorable since it causes a large friction on the paper P, and it has problems that it often allows several sheets of paper P to be completely overlapped when separating of the paper P has failed.
The present invention has been made with the aim of solving the above problems, and it is one object of the present invention to provide a paper separating unit which prevents the multiple-feeding of paper P, and an electronic printing apparatus which carries said paper separating unit.
The paper separating unit of the present invention which comprises a pick roller for picking paper from a paper container; a first feed roller for feeding said paper picked by said pick roller in order; a separate roller being pressed onto said first feed roller; a motor for driving said separate roller in the same rotational direction as that of said first feed roller; a drive system interlocking said separate roller with said motor; a torque limiter being interposed in said drive system; and a second feed roller for acceleratedly feeding paper which has passed through the gap between the first feed roller and the separate roller, is characterized in including a reverse-rotation preventing portion for preventing reverse-rotation of said separate roller when said motor is stopped, wherein said separate roller rotates together with said paper which is acceleratedly fed by said second feed roller.
The electronic printing apparatus of the present invention is characterized in comprising said paper separating unit, and further comprising a paper container for containing said paper, and a printing portion for printing on said paper acceleratedly fed by said second feed roller.
Therefore, by comprising said reverse-rotation preventing portion which prevents reverse-rotation of the separate roller which interlocking the paper fed by the second feed roller when the motor stopped, the electronic printing apparatus acts as follows:
When more than one sheet of the paper are picked up from the paper container, and fed into the gap between the first feed roller and the separate roller, only the top paper is allowed to be fed in its feeding direction by the first feed roller, while the remaining sheets of paper underneath the top paper are fed back in the opposite direction of its feeding.
While only the top paper is fed forward in the feeding direction, then its feeding rate is increased by the second feed roller when the motor is stopped. However, since the reverse-rotation preventing portion limits rotation of the separate roller which is driven in the reverse direction by the paper acceleratedly fed is limited in this direction, the paper is acceleratedly fed without interference of the separate roller and the first feed roller, at the same time, the remaining of paper once fed back into the paper container can not be re-fed into the gap between the first feed roller and the separate roller and to the second feed roller.
It is another object of the present invention to provide a concrete composition of said reverse-rotation preventing portion.
The reverse-rotation preventing portion is characterized in being a one-way clutch being interposed between the motor and the separate roller.
Therefore, the reverse-rotation of the separate roller is prevented by providing the one-way clutch which maintains the rotation of the separate roller while it is driven by the motor and races the separate roller when it is driven by the first feed roller.
The reverse-rotation preventing portion is characterized in that it includes a worm gear interlocked with said motor, and a gear interlocked with said separate roller and mating with said worm gear.
Therefore, since there is a directivity in the transmission of driving force between the worm gear and said gear so that it is impossible to transmit the driving force to the worm gear by rotating said mating gear, the reverse-rotation of the separate roller interlocked with the gear is prevented.
The reverse-rotation preventing portion is characterized in that it includes a ratchet gear connected with an arbitrary rotational axis of said drive system wherein the motor and the separate roller is interlocked, and a pawl engaging said ratchet gear.
Therefore, since the above constitution has a directivity of driving force similar to the combination of the worm gear and the mating gear described above so that it is impossible to transmit the driving force to the ratchet gear by driving the pawl, the reverse-rotation of the separate roller interlocked with the ratchet gear can be prevented.
The reverse-rotation preventing portion is characterized in that it includes a current applying portion for applying holding current to the motor to stop said motor, not for mechanically preventing the reverse-rotation of said separate roller as described above.
Moreover, said reverse-rotation preventing portion is characterized in that it is a motor control portion supplying a sufficient amount of current to stop said motor as described above.
Therefore, where the separate roller interlocked with the motor is driven in the reverse direction by the paper, the reverse-rotation of the separate roller is prevented by applying current to the motor to generate the same magnitude of force as that of the driving force.
The electronic printing apparatus and the paper separating unit disposed in the electronic printing apparatus of this invention are not to limit their application to the electrophotographic device described above and they are applicable to a device which includes a paper feeding unit, such as a facsimile, a scanner, a printer, and so forth.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.